1. Field of the Invention
The present invention relates to fireplace air heaters and more particularly to blower driven fireplace air heaters having front and rear manifolds connected by a plurality of air conduits so arranged that the air they convey passes at least twice near the fire built on the top thereof.
2. Description of the Prior Art
It is well known that a conventional fireplace is a very inefficient device for heating a room or a house, in that great quantities of air, besides that needed for combustion, are withdrawn from the room and exhausted up the chimney along with the flue gases. Cool air entering the room from the outside to replace that passing up the chimney results in the familiar phenomenon of a user with a warm front and a cold back.
As the fuel prices continue to rise, the necessity for converting the fireplace from an inefficient, decorative device to a more efficient, useful appliance has become imperative.
Of course, since the poor performance of the conventional fireplace has long been known, numerous ways to improve its heat output have been devised. One common solution is the convection heater that basically comprises a plurality of parallel C-shaped pipes, upon the base of which the fire is built. As the pipes are warmed by the fire, cool room air is drawn by convection into their bottom openings and is discharged from their top openings. To increase efficiency, a blower may be added which injects air into the bottom openings to thereby improve air circulation through the pipes, and a series of deflectors may be added which concentrate the hot flue gases on the top portion of the pipes, as disclosed in U.S. Pat. No. 3,955,553, granted May 11, 1976 to Soeffker.
Such devices suffer from the drawback that if the fire does not cover the base of all of the tubes, there may be a cold draft emitted by any tube not in contact with the fire. Making the fire larger to heat these tubes may result in a wasteful surplus of heat, and reducing the number of tubes so that only a small fire can be used may cause a cold room due to insufficient heating. Further, such devices make no provision for regulating the primary and secondary combustion air to the fire so that the fire will flare wastefully when the volatile substances in the wood are burned resulting in inefficient utilization of the fuel and increased amounts of pollutants emitted into the air.
Another solution proposed involves a blower driven, generally horizontal array of air tubes. This may involve one long air tube bent so that it partially encircles the fire as disclosed by U.S. Pat. No. 3,001,521 granted Sept. 26, 1961 to Reilly; or there may be a centrally located air tube supplying a plurality of parallel air delivery tubes, all of which pass beneath the fire as disclosed by U.S. Pat. No. 3,942,509 granted Mar. 9, 1976 to Sasser.
As before, later devices have many drawbacks and they too provide no method for controlling the draft to the fire to regulate the rate at which the fuel burns. Further, they are difficult and expensive to manufacture since they involve bending air tubes which are likely to be made of heat resistant steel. In addition, they are of one-piece or welded construction which makes impossible quick and inexpensive replacement of a damaged or burned out air tube. Another drawback of these devices is that they provide no effective means for preventing the coals and unburned fuel from dropping through the grate, resulting in a portion of each charge of fuel being wasted. Finally, as all the referenced patents disclose, cleaning the fireplace of ashes and waste material is a tedious, difficult, time consuming and dirty job involving either inconvenient sweeping beneath and around the device or dismantling and removing it from the fireplace each time ash removal is required.